We propose to compare three methods (flow interruption, forced oscillation and isovolume pressure flow curves) for measuring the relationship of pulmonary resistance (R sub L) to lung volume and elastic recoil. We shall also determine the contribution of extrathoracic airway resistance to R sub L in each of these techniques. The relationship of thoracic wall resistance to lung volume will be determined by forced oscillation. We will examine the effect of lung volume, subject generated flow, and the amplitude and frequency of forced oscillation on the impedance and phase relationships of the lung and respiratory system in normal subjects and patients with chronic obstructive lung disease (COLD). We propose that the measurement of impedance and phase may differentiate patients with increased resistance due to loss to elastic recoil from patients with increased resistance due to bronchial disease. Measurement of the response to forced oscillation may identify subjects who have frequency dependence of lung compliance and is a more suitable test for clinical use. We will also examine the contribution of airway compliance to the frequency and flow dependence of resistance determined by the oscillation technique.